Robotnik is the villain of the Sonic universe in most games, a genius scientist with an IQ of 300. He is always attempting to destroy parts of the world to make it home to his super-city so he can then attain world domination, only to be stopped by Sonic and his friends every time. On two occasions he has used a scientific experiment and an ancient monster to achieve his plans, both of which fail (Shadow the Hedgehog and Chaos, respectively).

He doesn't fight himself all that often and usually builds robots to carry out his dirty work, powered by small animals. Some of his more notable inventions include the Egg Carrier (a flying fortress), the Death Egg (a space station), the Egg Mobile (his aerial transportation vehicle), Metal Sonic (a robotic clone of Sonic), among many other things.

His grandfather was also a genius scientist, Gerald Robotnik, who originally created Shadow the Hedgehog via Black Doom's DNA.